Hmm...have you really popped valve covers and checked for broken studs? They might be loose or you might have a case of "uneven mating surface". Quite common problem on 930's.

Interesting enough, it's often nr. 5 that leaks...mine did it too! it must be something with bad cooling/airflow.

Are you sure it's the cylinder and not the oil return tube? The tubes are notorious for leaking and there are two piece tubes for replacing them with engine still together.

It's pretty easy to pull the lower valve covers and check for broken studs. You should be able to do it in about an hour.

If you do have a broken stud, clean the engine before you pull the heads and cylinders since you don't want to split the case.

If you don't have any broken studs, you could clean the bottom of the engine with it still in the car and go back for the inspection.

Great stuff, thanks guys.

The car is in the workshop having some interior work done so I can't quckly check all the great ideas you have given me. It should be back next week and I'll update you all with some photos.